This invention relates to fabrication of arrays of physically raised structures on glass substrates and, more particularly, to a method and apparatus for producing such a arrays of raised structures through use of electron-beam exposure apparatus.
Micro-arrays of physically protruding structures from a planar surface have uses in a number of fields of application, including biology, optics, displays and printing. A variety of techniques have been utilized to fabricate such arrays, including lithography/etching and laser processing. For example, during the production of semiconductor devices, pedestal and other raised shapes have been produced through the use of a combination of lithography, followed by either wet or plasma etching, to leave the protruding structures.
Recently, fabrication of structures in silicon-oxide have been tried, using a low-energy electron-beam stimulated reactions. More specifically, by exposing a finely focused, high-energy electron beam onto a thin silicon oxide layer, followed by either wet etching or a thermal desorption procedure, nanometer-sized windows were formed in a silicon-oxide layer. Further, etching of a thin silicon oxide layer has been reported using a low energy electron beam stimulated reaction. Such reaction was accomplished using a scanning tunneling microscope and thermal desorption. This method of nano-fabrication enabled an array of pin holes and trenches to be produced in the thin silicon oxide layer. See Li et al., xe2x80x9cNano-Fabrication on Si Oxide With Scanning Tunneling Microscope: Mechanism of the Low-Energy Electron-Stimulated Reaction,xe2x80x9d Applied Physics Letters, Vol. 74, No. 11, Mar. 15, 1999, Pages 1621-1623.
Maruno et al. have also reported selective thermal desorption of a silicon dioxide film of less than one nanometer in thickness that was induced by a focused electron beam. Their findings indicated that clean, silicon opened windows were formed in the silicon dioxide film and that the surface morphology depended on electron dose, oxide film thickness and desorption temperature. See xe2x80x9cObservation of Selective Thermal Desorption of Electron Stimulated SiO2 With a Combined Scanning Reflection Electron Microscope/Scanning Tunneling Microscopexe2x80x9d Journal of Applied Physics, Vol. 82, No. 2, Jul. 15, 1997, Pages 639-643.
Another e-beam patterning technique in the prior art is described by Wendel et al. in Applied Physics Letters, Vol. 67, page 3732 (1995) where contamination build-up is used to accomplish the patterning in a manner similar to plasma deposition. The deposition occurs as a result of polymerization of contaminating species, such as C, O and H.
Two of the above-indicated references describe a subtractive process for creating a physical feature in a silicon oxide layer. The third describes an additive process that utilizes contaminant particles. By contrast, there is a need for a non-subtractive method for creating protruding features from silicon oxide surfaces that retain the transparency and characteristics of the underlying substrate. Such features may be utilized to create finely pointed emission sources, barriers between adjacent pixel sites in flat panel displays, etc.
The method of the invention produces protruding features on a glass layer. Initially, a conductive layer is applied to the glass layer and is coupled to a source of reference potential. This conductive layer prevents a build-up of electrons in the glass layer when it is exposed to an electron beam. Thereafter, an electron beam is directed at combined layers in areas where protruding features are to be produced. The energy, current density and duration of application of the electron beam are controlled so as to create a melt/softened region within the glass layer. Such softening and differences in expansion rates between the softened glass and the surrounding glass causes a protruding feature to appear on the surface of the glass layer.